Since hydroxycarboxylic acids are useful as a raw material for polymers or an intermediate for medicines, a method for effectively producing hydroxycarboxylic acids have been demanded.
As an example, glycolic acid (α-hydroxyacetic acid) can be mentioned. Glycolic acid has been used as a raw material for cleaning agents or cosmetics, but has recently received attention as a raw material for polyglycolic acid which is useful as a gas barrier polymer or a medical polymer. The reason why glycolic acid has received attention as a gas barrier material is that a layer of polyglycolic acid has high oxygen barrier property and performance as a material for packing food or carbonated beverage which can easily spoil in the presence of oxygen.
Glycolic acid of a chemically synthesized product which is currently commercially available contains quite a few impurities, which is a problem when used as a raw material for polymers in view of purity. This is because these impurities inhibit a dehydrating condensation reaction of glycolic acid, and also methoxy acetate which is one of those impurities is a compound suspicious of carcinogenic potential, thus being desirable not to be included in a packing material for food or beverage. It is technically possible to remove impurities by purification, but such the purified products are high in cost and thus are not practical as a raw material for packing at low cost.
In order to avoid the aforementioned problems given in glycolic acid of chemically synthesized products, a production of glycolic acid according to a biomethod employing ethylene glycol as a raw material has been attempted. In Patent Document 1 and Patent Document 2, there has been disclosed a method for producing glycolic acid by a microorganism, which includes culturing yeast belonging to genus Pichia, genus Rhodotorula, genus Sporobolomyces, genus Kluyveromyces or genus Torulopsis, a strain belonging to genus Nocardia, a strain belonging to genus Rhodococcus, or an Escherichia coli B strain in a culturing medium containing ethylene glycol and separating and collecting glycolic acid from the culturing broth. Among the methods for producing glycolic acid as described in Examples of Patent Document 1 and Patent Document 2, a method employing Pichia naganishii gives the highest accumulation concentration of glycolic acid, and 35.3 g/L of glycolic acid is obtained by a reaction for 30 hours. In regard to the production of glycolic acid with the use of Pichia naganishii, it has been reported in Non-Patent Document 1 that 105 g/L of glycolic acid can be obtained by a reaction for 120 hours with further improved reaction conditions.
In Patent Document 3, it has been described that it is possible to produce hydroxycarboxylic acids including glycolic acid from a raw material like aliphatic polyhydric alcohols having a hydroxyl group at the end such as ethylene glycol, by using a microorganism in which a gene encoding lactaldehyde reductase and a gene encoding lactaldehyde dehydrogenase are introduced in the form of plasmid so as to impart or enhance an activity of those enzymes, as well as described that an ability to produce glycolic acid is improved by disrupting a gene encoding glycolate oxidase contained in a microorganism so as to inactivate an activity of the enzyme.
In a reaction for producing hydroxycarboxylic acids including glycolic acid by the above-mentioned conventional methods, an amount of microbial cell required for the reaction is large, which thereby causes problems such as an increase in the production cost, contamination by impurities derived from the microbial cells, and requiring so much work and cost for disposing the microbial cells after the production of hydroxycarboxylic acids.
In a method for producing ketone from alcohol using an oxidase, a technique as described below that oxidized-type nicotinamide adenine dinucleotide (hereinafter, may be referred to as NAD) needed for a reaction is regenerated from reduced-type nicotinamide adenine dinucleotide (hereinafter, may be referred to as NADH) produced in accompany with the reaction has been employed. That is, there are a method of combining two reactions of an oxidation reaction to produce a purposed ketone and a reduction reaction of ketone to regenerate NAD are combined, a technique combined with a reduction reaction of oxoglutaric acid by glutamic acid dehydrogenase, and the like.
In the above technique to regenerate NAD, there may been mentioned problems that it is needed to add a reaction substrate to regenerate NAD into the reaction system and that by-products from the reaction to regenerate NAD are accumulated in the reaction system.
In the production of ketone from alcohol, there has been disclosed a method to make up for the above problems, in which NADH dehydrogenase is used for regenerating NAD by a reduction of molecular-form oxygen via respiration chain of a microorganism to produce water (Patent Document 4), but actual examples of microorganisms having enhanced activity of the enzyme has not been reported.
[Patent Document 1] Japanese Patent Laid-open No. H10-174593
[Patent Document 2] Japanese Patent Laid-open No. H10-174594
[Patent Document 3] International Publication Pamphlet No. WO 2005/106005
[Patent Document 4] Japanese Patent Laid-open No. 2005-218349
[Non-Patent Document 1] Biosci. Biotechnol. Biochem., Vol. 65(10), pp. 2265-2270, (2001)